Fire extinguishing powders



United States Patent 3,350,306 FIRE EXTINGUISHING POWDERS Jean C. Alleton, Paris, France, assignor to Societe dEtudes Chimiques Pour llndustrie et IAgriculture, Paris, France No Drawing. Filed Dec. 16, 1963, Ser. No. 330,549 Claims priority, appiication France, Dec. 21, 1962, 919,442 16 Claims. (Cl. 252-7) This invention relates to improved fire extinguishing powders which remain free-flowing and do not cake even after a long period of storage.

It is well known that alkali metal bicarbonates are hygrosopic and have a tendency to cake during storage; therefore when used for dry chemical fire extinguishing powders, they are as ageneral rule treated with an anticaking agent, otherwise they would soon become unsuitable. Various water-repellent agents have been proposed as anti-caking additives (water-insoluble waxes, silicones, etc.) for preparing fire extinguishing powders based on alkali metal bicarbonates, but in practice water-insoluble salts of fatty acids are generally used, in particular calcium or magnesium soaps, and especially calcium stearate. However, all these products are relatively expensive for use in fire extinguishing powder. This is particularly evident in the case of potassium bicarbonate because it is much more hygroscopic than sodium bicarbonate and requires the addition of a larger amount of anti-caking agent. The addition of an increased quantity of anti-caking agent has another drawback: fatty acid salts being combustible tend, if used in excessive amounts, to reduce the extinguishing power of the powder.

Aside from the absence of caking, fire extinguishing powders must also be and remain free-flowing right up to their utilization. The addition of the aforementioned anti-caking agents is not sulficient to convey this property to alkali metal bicarbonates for, while they prevent caking, they cannot keepthe powder from lumping when projected under pressure. Therefore, usually besides the anti-caking agent, a certain amount of finely divided inert substances such as starch, silicia, various silicates as, for example, talc, mica, etc., are conventionally added to the alkali metal bicarbonates. However, these inert products greatly increase the hygroscopicity of the powder thereby requiring in turn a greater quantity of anti-caking additive.

A principal object of this invention therefore is to avoid these disadvantages of the prior art by providing an inexpensive additive which acts to prevent caking and also to increase the flowability of the alkali-metal-bicarbonate fire extinguishing powder.

Upon further study of the specification and claims other objects and advantages of the prevent invention will become apparent.

It has now been discovered that the addition of watersoluble inorganic salts or iron (ferrous or ferric salts) to an alkali metal bicarbonate prevents it from caking and substantially increases its free-fiowing properties. Thus, a fire extinguishing powder having the characteristics required can be prepared by treating alkali metal bicarbonate with one agent only.

According to the process of the present invention iron sulfate is preferably used and, more particularly, technical grade salts which are very inexpensive by-products; nevertheless, other water-soluble inorganic iron salts as well as mixtures thereof may be used, such as nitrates, halides, and thiosulfate. By water-soluble salts I mean a salt of which at least 20 g. can be dissolved in 100 g. of water at room temperature (about 20 C.).

The fire extinguishing powders disclosed in the present invention are prepared by adding a minor quantity of iron salt of at least about 0.5 to preferably about 10% by weight (calculated as anhydrous iron salt) relative to the alkali metal bicarbonate treated. It has been observed that the addition of a quantity higher than about 10% of iron salt does not substantially improve the effect as compared with smaller quantities. In practice, preferably at least about 2% up to about 5% by weight are used for treating potassium bicarbonate, whereas smaller quantities as, for example, from about 0.5 to about 3% are sufiicient to treat sodium bicarbonate which is less hygroscopic. That is, for each 100 parts by weight of an alkali metal bicarbonate, there is added 0.5-l0 parts by weight of any anti-caking inorganic water-soluble iron salt, the ratio of said iron salt to said bicarbonate being, in parts by weight, 0.5:100 to 10:1'00, respectively. Similarly, 2 to 5 parts by weight of iron salt is used for 100 parts by weight of potassium bicarbonate or 0.5 to 3 parts by weight of iron salt to 100 parts by weight of sodium bicarbonate.

It is of course possible to combine the action of iron salts to that of other agents already known to prevent caking and to increase flowability; still, when such is the case the quantities of agents added are always.considerably lower than those used as a general rule. Consequently, the expression consisting essentially of employed herein includes compositions having other anti-caking and flow-promoting agents, as well as any other additive used in fire extinguishing powders.

Tests for the extinguishment of gasoline fires have shown that the addition of inorganic iron salts in the quantities hereabove specified does not affect the fire fighting potential of alkali metal bicarbonates.

Various methods may be employed for preparing fire extinguishing powders of the present invention. According to a preferred embodiment, a concentrated iron salt aqueous solution, advantageous at least at about of saturation, is sprayed on the bicarbonate to be treated. This spraying operation may be effected more economically during the manufacture of bicarbonate prior to the drying of this salt. It may also be performed independently in a separate unit in which case a very concentrated solution, preferably even saturated in iron salt, is used so as to reduce the amount of water to be removed by subsequent drying.

It is also possible to add solid iron salt during the grinding of alkali metal bicarbonate because the traces of water always contained in the commercial product, about 0.5% by weight, will as a rule with sufiicient grinding be enough to dissolve the iron salt at-least partially, thus improving its distribution on the particles of bicarbonate.

It is thus evident that it is necessary to at least partially coat substantially all (at least 75% by Weight) if not all of the alkali metal bicarbonate powder in order to obtain the advantages of this invention. For this coating step, the particle size range of uncoated alkali metal bicarbonates is about 1000 microns (16 mesh of the Tyler Standard Screen Scale Sieves Series) to microns mesh sieve), preferably about 500 microns (32 mesh sieve) to 100 microns (150 mesh sieve).

In general, the fire extinguishing powder is used in a particle size range such that all the powder passes through a 150 micron sieve (100 mesh of the Tyler Standard Screen Scale Sieves Series) and that 80% of the powder passes through a 44 micron sieve (325 mesh sieve).

The fire extinguishing powder of this invention can be used in any commercial type of apparatus for projecting or spraying a dry chemical fire extinguishing powder under gas pressure.

The fire extinguishing powders disclosed in the present invention and prepared by addition of a water-soluble iron salt have an outstanding advantage compared to those obtained by treating the bicarbonate with Water-insoluble agents inasmuch as the powders of this invention are in the form of a more homogeneous mixture with wellcoated particles.

Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The following preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the specification and claims in any way whatsoever.

Example 1 An iron sulfate saturated aqueous solution (technical grade containing 23% Fe and 44% S was sprayed onto potassium bicarbonate crystals of a particle size of about 500 to 100 microns in such quantity that the added iron sulfate amounts to 2% by weight of the potassium bicarbonate treated. The resulting product was dried until it contains 0.1% of water by weight, and then ground so that the total quantity of powder obtained passes through a 100 micron screen (150 mesh of the Tyler Standard Screen Scale Sieves Series), with'80% of the particles measuring less than 44 microns, i.e. passing through a 325 mesh sieve.

The product obtained is in the form of a perfectly evenly-colored yellow powder, but light hued enough to make it possible to give it another color for identification purposes.

This powder designated hereinbelow as A was then submitted to different tests at the same time as two other powders (B and C) based on potassium bicarbonate but which had been treated by the usual known methods.

Powder B was prepared by adding to potassium bicarbonate 3% by weight of calcium stearate; the mixture was then ground to same size as powder A.

Powder C was prepared by adding to potassium bicarbonate 3% by weight of calcium stearate and 1% of silica; the mixture was then ground to the same size as powders A and B.

Powders B and C have the same moisture content as powder A, that is 0.1%.

Several samples of each of the three powders were weighed, then placed in an atmosphere of 80% relative humidity at 25 C. and left for 24 hours. Each sample was then weighed and the moisture percentage absorbed by weight of dry powder was calculated.

The following table illustrates the average figures obtained for several samples:

Percent Powder A 0.1 Powder B 3 Powder C 12 The free-flowing characteristics of each powder were measured on fresh powders, that is to say, before any storage. The following figures illustrate the time in seconds that 500 g. of powder took to pass through a circular opening measuring 25 mm. diameter:

Powder A 7.5 (average of 10 measurements).

Powder B Flow practically impossible.

Powder C 17.4 (average of 10 measurements).

Example 2 A powder based on potassium bicarbonate was pre pared according to the method of Example 1, but in such manner that the content of iron sulfate amounts to 5% instead of 2%.

The powder obtained designated hereinbelow as A was then placed in an atmosphere of 80% relative humidity at 25 C. and left for 65 hours. Powders B and C prepared as specified in Example 1 were treated under the same conditions as powder A The moisture absorbed by the three powders was then calculated, and the following figures illustrate the average results obtained:

The .time required for powder A to flow under the same conditions as described in Example 1 was 11 seconds (average of 10 measurements).

Example 3 A powder based on potassium bicarbonate was prepared under the same conditions as Example 1, but in such manner that in addition to the 2% content of iron sulfate it contains 1% calcium stearate.

A sample of this powder was weighed, then placed in an atmosphere of relative humidity at 25 C., and left for 24 hours. The sample was then weighed and the moisture percentage absorbed was calculated. The gain in weight was 3.8% (average of several measures) which is a value close to the gain in weight observed for the powder which contained 3% calcium stearate.

The free-flowing characteristics of the fresh powder were such that when measured under the same conditions as in Example 1, the time required was 8.7 seconds. Thus, the result obtained with this powder is substantially improved in comparison to that of powder B which contained 3% of calcium stearate.

Example 4 Powders based on potassium bicarbonate were prepared under the same conditions as in Example 1, but the ferric sulfate solution was replaced by solutions of other iron salts, ferric nitrate and ferrous sulfate, in such an amount that the treated product contains 2% of anhydrous iron salt.

Samples of these powders were placed in an atmosphere of 80% relative humidity of 25 C. and left for 24 hours. The moisture percentage absorbed was then calculated.

The powder treated with a ferrous sulfate solution gained 3.5% by weight and the powder treated with a ferric nitrate solution gained 4.1%

The use of the fire extinguishing powders of this invention is now described.

55 liters of essence F (mineral spirit having a boiling range from to C. under normal pressure) were poured into a round pan measuring 1.4 m. diameter, ignited and left to burn for one minute. The fire was then attacked using an extinguisher shell containing 9 kg. of potassium bicarbonate powder prepared according to Example 1 and having a 3.5 mm. diameter discharge nozzle. To project the powder onto the fire, nitrogen Was fed into the apparatus through a pressure-reducing valve so that the operating pressure was maintained at 10 kg.cm.

The table hereunder illustrates the results of a series of tests performed indoors in the above-mentioned conditions, the figures given being the average of 12 measure- The preceding examples repeated with different alkali metal carbonates and different water-soluble iron salts yield similar results.

From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications. Consequently, such changes and modifications are properly, equitably, and intended to be, within the full range of equivalence of the following claims.

What is claimed is:

1. A free flowing alkali metal bicarbonate fire extinguishing powder consisting essentially of 100 parts by weight of an alkali metal bicarbonate and 0.5- parts by weight of an anti-caking inorganic water-soluble iron salt, substantially all the alkali metal bicarbonate powder being at least partially coated with said iron salt.

2. A fire extinguishing powder as defined in claim 1, wherein the inorganic water-soluble iron salt is iron sulfate.

3. A free flowing alkali metal bicarbonate fire extinguishing powder consisting essentially of 100 parts by weight of potassium bicarbonate and 25 parts by weight iron sulfate, substantially all the potassium bicarbonate powder being at least partially coated with the iron sulfate.

4. A free flowing alkali metal bicarbonate fire extinguishing powder consisting essentially of 100 parts by weight of sodium bicarbonate and 05-3 parts by weight of iron sulfate, substantially all the sodium bicarbonate powder being at least partially coated with the iron sulfate.

5. A process for improving the anti-caking and freefiowing properties of fire extinguishing powders of alkali metal bicarbonates, which process comprises the steps of 1) spraying a concentrated aqueous solution of an anti-caking inorganic water-soluble iron salt onto a mass of alkali metal bicarbonate particles in a ratio of 05-10 parts by weight of anhydrous iron salt to 100 parts by weight of said bicarbonate particles; (2) drying the resultant coated mass of bicarbonate particles; and (3) grinding the resultant dried mass to a powder.

6. A process for improving the anti-caking and freeflowing properties of fire extinguishing powders of alkali metal bicarbonate, which process comprises the addition of an anti-caking inorganic water-soluble iron salt while said bicarbonate is being ground to a powder, and continuing the grinding for a suflicient time to allow traces of water associated with the bicarbonate to dissolve some of said iron salt, thereby coating the bicarbonate powder, the ratio of iron salt to bicarbonate being in parts by weight 0.5: 100 to 10: 100 respectively.

7. A process for extinguishing fires, which process comprises projecting onto said fire a free flowing alkali metal bicarbonate fire extinguishing powder consisting essentially of 100 parts by weight of an alkali metal bicarbonate a d 0540 P rts y e t f a a ti-c g inorganic.

water-soluble iron salt, substantially all the alkali metal bicarbonate powder being at least partially coated with said iron salt.

8. The process of claim 7, wherein the water-soluble iron salt is iron sulfate.

9. A process for extinguishing fires, which process comprises projecting onto said fire a free flowing alkali metal bicarbonate fire extinguishing powder consisting essentially of parts by weight of potassium bicarbonate and 25 parts by weight iron sulfate, substantially all the potassium bicarbonate powder being at least partially coated with the iron sulfate.

10. A process for extinguishing fires, which process comprises projecting onto said fire a free flowing alkali metal bicarbonate fire extinguishing powder consisting essentially of 100 parts by weight of sodium bicarbonate and 0.53 parts by weight of iron sulfate, substantially all the sodium bicarbonate powder being at least partially coated with the iron sulfate.

11. A fire extinguishing powder as defined by claim 1 wherein said alkali metal bicarbonate, is selected from the group consisting of sodium and potassium bicarbonates.

12. A fire extinguishing powder as defined by claim 1 wherein said iron salt is selected from the group consisting of iron nitrate, iron halide, and iron thiosulfate.

13. A fire extinguishing powder as defined by claim 11 wherein said iron salt is selected from the group consisting of iron nitrate, iron halide, and iron thiosulfate.

14. A fire extinguishing process as defined by claim 7 wherein said alkali metal bicarbonate is selected from the group consisting of sodium and potassium bicarbonates.

15. A fire extinguishing process as defined by claim 7 wherein said iron salt is selected from the group consisting of iron nitrate, iron halide, and iron thiosulfate.

16. A fire extinguishing process as defined by claim 14 wherein said iron salt is selected from the group c0nsisting of iron nitrate, iron halide, and iron thiosulfate.

References Cited UNITED STATES PATENTS 387,915 8/1888 Penrose et al. "2527 2,030,583 8/1936 Haas et al. 252385 XR 2,912,379 11/1959 McCracken 2527 3,033,291 5/1962 Wieslander 2527 XR LEON D. ROSDOL, Primary Examiner.

JULIUS GREENWALD, DONALD E. CZAJA,

Examiners,

M. WE N LA T, As i t n E m n r. 

1. A FREE FLOWING ALKALI METAL BICARONATE FIRE EXTINGUISHING POWDER CONSISTING ESSENTIALLY OF 100 PARTS BY WEIGHT OF AN ALKALI METAL BICARBONATE AND 0.5-10 PARTS BY WEIGHT OF AN ANTI-CAKING INORGANIC WATER-SOLUBLE IRON SALT, SUBSTANTIALLY ALL THE ALALI METAL BICARBONATE POWDER BEING AT LEAST PARTIALLY COATED WITH SAID IRON SALT. 